Method and apparatus for evaluating ion implant dosage levels in semiconductors

Abstract

An apparatus (10) designed to evaluate ion implantation levels in semiconductor samples (42) is disclosed. The device includes an intensity modulated pump laser beam (22) and a probe beam (62) having a different wavelength than the pump beam. The two laser beams are focused on a coincident spot on the surface of the sample. Detectors (80, 96) are provided for measuring the non-modulated reflected power of the pump and probe beams. In addition, the modulated reflected power of the probe beam, that is in phase with the intensity modulated pump beam, is also measured. These three independent measurements are utilized to derive the implant dosage level in the semiconductor sample.

I claim: 
     
       1. An apparatus for evaluating the implant dosage level of a semiconductor sample having an oxide surface coating comprising: means for emitting an intensity modulated pump beam of radiation;   means for emitting a probe beam of radiation having a different wavelength than the pump beam of radiation;   means for focusing the pump and probe beams at a substantially coincident spot on the surface of the sample;   means for measuring the modulated reflected power of the probe beam that is in phase with the intensity modulated pump beam;   means for measuring the nonmodulated reflected power of the probe beam;   means for measuring the nonmodulated power of the reflected pump beam; and   means for processing the three reflected power measurements to evaluate the implant dosage level in the semiconductor sample.   
     
     
       2. An apparatus as recited in claim 1 wherein said processor utilizes the reflected power measurements to calculate the thickness of a material layer created by the implantation and wherein the thickness of the material layer is correlated to the dosage level. 
     
     
       3. An apparatus for evaluating the implant dosage level of a semiconductor sample having an oxide surface coating and an internal amorphous material layer created by a high dosage level comprising: means for emitting an intensity modulated pump beam of radiation;   means for emitting a probe beam of radiation having a different wavelength than the pump beam of radiation;   means for focusing the pump and probe beams at a substantially coincident spot on the surface of the sample;   first detector means for measuring the power of the reflected probe beam, said first detector means for measuring the modulated reflected power of the probe beam that is in phase with the intensity modulated pump beam, said first detector means for also measuring nonmodulated reflected power of the probe beam.   second detector means for measuring the nonmodulated power of the reflected pump beam; and   means for processing the three reflected power measurements obtained by the first and second detector means to derive the thickness of the amorphous material layer and thereafter correlating the derived thickness of the amorphous material layer to the implant dosage level in the semiconductor sample.   
     
     
       4. An apparatus as recited in claim 3 wherein said processor compares the derived thickness of the amorphous material layer to the derived thickness of the amorphous material layer of other semiconductor samples having a known implant dosage level. 
     
     
       5. An apparatus as recited in claim 3 wherein said semiconductor sample is formed from crystalline silicon and the amorphous material layer is amorphous silicon. 
     
     
       6. A method for evaluating the implant dosage level of a semiconductor sample having an oxide surface coating, said method comprising the steps of: generating an intensity modulated pump beam of radiation;   generating a probe beam of radiation having a different wavelength than the pump beam of radiation;   focusing the pump and probe beams at a substantially coincident spot on the surface of the sample;   measuring the modulated reflected power of the probe beam that is in phase with the intensity modulated pump beam;   measuring the nonmodulated reflected power of the probe beam;   measuring the nonmodulated power of the reflected pump beam; and   processing the three reflected power measurements to evaluate the implant dosage level in the semiconductor sample.   
     
     
       7. A method as recited in claim 6 wherein said processing step includes calculating the thickness of a material layer created by the implantation and wherein the thickness of the material layer is correlated to the dosage level. 
     
     
       8. A method for evaluating the implant dosage level of a semiconductor sample having an oxide surface coating and an internal amorphous material layer, said method comprising the steps of: generating an intensity modulated pump beam of radiation;   generating a probe beam of radiation having a different wavelength than the pump beam of radiation;   focusing the pump and probe beams at a substantially coincident spot on the surface of the sample;   measuring the modulated reflected power of the probe beam that is in phase with the intensity modulated pump beam;   measuring the nonmodulated reflected power of the probe beam;   measuring the nonmodulated power of the reflected pump beam; and   processing the three reflected power measurements to derive the thickness of the amorphous material layer and thereafter correlating the derived thickness of the amorphous material layer to the implant dosage level in the semiconductor sample.   
     
     
       9. A method as recited in claim 8 further including the step of comparing the derived thickness of the amorphous material layer to the derived thickness of the amorphous material layer of other semiconductor samples having a known implant dosage level. 
     
     
       10. A method as recited in claim 8 wherein said semiconductor sample is formed from crystalline silicon and the amorphous material layer is amorphous silicon.